There are many processes in which a heated fluid circulating in a closed loop must have a major portion of the heat removed therefrom. One example of such a process is steam flowing in evaporators in a pulp and paper mill. Typically, the steam from the last effect of evaporators passes to a condensing tower wherein the steam is passed between pairs of dimpled condensing plates, while a film of water flows over the exterior of the condensing plates to remove heat from the steam. The water is typically provided in a single closed loop system, and is connected to a cooling tower or the like. In such operations it is essential to provide the necessary degree of cooling of the steam to effect condensation thereof, but typically the low-grade heat given up by the steam as it condenses is wasted.
According to the present invention, a method and assembly are provided which minimize the waste of heat from the steam condensed in the condensing tower. This is accomplished by passing process inlet water from a clean water source through the condensing tower, the water being warmed up so that less heat need be added thereto to use the water in an appropriate operation within the plant. For instance it is necessary to heat the water that is used in the pulp washing steps in a pulp and paper mill, therefore passing water from a clean water source (e.g. a river) through the condensing tower to heat the water greatly facilitates the utilization of that water for subsequent pulp washing.
While it is thus highly desirable to utilize water from a clean water source as the cooling water in a condensing tower, the temperature of the water from the source varies greatly depending upon the season, and the volume of water utilized is not sufficient to provide all the necessary condensing required. Therefore, according to the present invention two flows of condensing liquid are provided in a condensing tower. The first flow is from the source of clean water, with an outflow to a pulp washing station or the like, while the second flow--which is always maintained segregated from the first flow--is provided in a typical closed loop, such as a conventional loop containing a cooling tower. Apparatus is provided associated with the condensing tower for varying the amount of water flowing in the first and second flows depending upon the temperature of the clean water source.
The apparatus according to the invention includes a vertical cylindrical vessel having a plurality of pairs of condensing plates disposed therein, preferably in an annular arrangement defining a central circular-cross-section interior opening. Steam to be condensed passes between the condensing plates of each pair. First and second water inlets are provided at the top of the vessel, separated by a radially extending fixed baffle, while first and second liquid outlets are disposed at the bottom of the vessel separated by another radially extending fixed baffle. A vertical central shaft extends in the interior of the vessel with a top movable baffle and a bottom movable baffle mounted thereto. The shaft is rotated to vary the positions of the top and bottom movable baffles with respect to the first and second water inlets and outlets to thereby vary the number of condensing plates associated with the first and second liquid flows.
It is the primary object of the present invention to provide an effective method and apparatus for the simultaneous heating of process inlet water from a clean water source, and removal of heat from a heated fluid (such as steam) passing in a closed circulatory loop. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.